The present invention relates to an image forming apparatus and more particularly to a charge roller included in an image forming apparatus and rotatable in contact with the surface of an image carrier, which is driven such that the surface moves, for thereby charging the surface of the image carrier. The charge roller is made up of a core and an elastic body affixed to the periphery of the core and formed mainly of rubber.
Generally, an electrophotographic copier, printer, facsimile apparatus, multiplex machine or similar image forming apparatus includes a charge roller made up of a core and an elastic body affixed to the core for uniformly charging the surface of an image carrier. An AC-biased DC voltage is applied to the charge roller.
Stearic acid, which is a specific treatment aid, is usually added to rubber that constitutes the elastic body of the charge roller. During the fabrication of the charge roller, stearic acid prevents rubber from sticking to, e.g., a pair of rollers used to knead rubber. However, the problem with stearic acid is that it is separated on the surface of the charge roller due to the influence of humidity and temperature. As the charge roller is repeatedly used over a long period of time, separated stearic acid is apt to aggravate the contamination of the charge roller and thereby make the charging of the image carrier and therefore images defective.
A cleaner formed of foam urethane or felt, for example, may be held in contact with the charge roller in order to clean the surface of the charge roller. The cleaner, however, must be angularly moved by a moving device in its lengthwise direction so as to obviate irregular cleaning, increasing the cost of the image forming apparatus.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 9-43936 and 11-194533.
It is therefore an object of the present invention to provide an image forming apparatus capable of effectively reducing the defective charging of an image carrier ascribable to stearic acid separated on the surface of a charge roller, and a charge roller therefor.
In accordance with the present invention, an image forming apparatus includes an image carrier to be driven such that its surface moves. A charge roller is made up of a core and an elastic body affixed to the periphery of said core. The charge roller charges the surface of the image carrier by being applied with an AC-biased DC voltage while rotating in contact with the surface. The major component of the elastic body is rubber. An exposing device exposes the surface of the image carrier charged by the charge roller imagewise to thereby form a latent image thereon. A developing device develops the latent image with toner to thereby form a corresponding toner image. A fixing device fixes the toner image transferred to a recording sheet. Stearic acid is added to rubber constituting the elastic body in an amount of 1 wt % or less.
Also, in accordance with the present invention, a charge roller for charging the surface of an image carrier while rotating in contact with the surface is made up of a core and an elastic body affixed to the periphery of the core and formed mainly of rubber. Stearic acid is added to rubber constituting the elastic body in an amount of 1 wt % or less.